458 Prof. Scheerer on the Separation of Lime and Magnesia. 



it ought to increase in weight 3"5 per cent, on being heated in 

 the air and converted into sesquioxide ; but in fact it lost weight. 

 AVohler thinks, therefore, that it contains an admixture of some 

 binoxide of chromium, CrO^. 



The method of separating lime from magnesia by means of 

 oxalate of ammonia, is not available where only small quantities 

 of lime are present. In a solution of magnesia containing 1 per 

 cent, of lime, oxalate of ammonia produces no precipitate. 

 The following method, which was originally given by Rose, is 

 recommended by Scheerer* as being accurate for the detection 

 and separation of small quantities of lime. Both the earths 

 converted into sulphates are dissolved in water, and alcohol 

 added with continued agitation until a faint but permanent tur- 

 bidity results. After standing some hours, all the lime is preci- 

 pitated as gypsum, which is filtered, aud washed with a mixture 

 of alcohol and water. AVheu too much alcohol is added, some 

 sulphate of magnesia is precipitated. In this case the sulphates 

 may be redissolved and reprecipitated with alcohol, or the lime 

 precipitated with oxalate of ammonia ; the magnesia not being 

 present in excess does not prevent its precipitation. 



By this method Scheerer detected small quantities of lime in 

 some magnesian minerals with which he had formerly deter- 

 mined the equivalent of magnesium. The results obtained gave 

 for the equivalent of magnesium 12'04 to 12'06. By allowing 

 for the trace of lime present, the true number would be i2'0, if 

 not slightly under. It is possible that in Dumas's late experi- 

 mentstj in which he found numbers varying from 12 to 12'5, 

 the magnesian salt employed by him. may not have been free 

 from lime. 1 per cent, of calcium in carbonate of magnesia 

 would make a difference in the equivalent of from O'l to 0'3, 



The following observations on silicon have been made by 

 Wohler and DevilleJ. Silicon, like boron and titanium, can 

 absorb nitrogen directly, as is proved by the following experiment. 

 A small Hessian crucible containing some crystallized silicon 

 was placed in a larger crucible, the interstices packed with 

 recently ignited charcoal powder, the cover of the large crucible 

 carefully luted down, and the whole exposed to the temperature 

 of a coke fire for an hour. 



On cooling, the silicon was found to be changed into a porous 

 bluish mass, covered with a fibrous crust resembling mountain 

 cork. Viewed under the microscope, it was seen to be com- 

 posed of numerous dark tombac-coloured crystals, resting on 



* Liebig's Annalen, May 1859. 



t Phil. Mag. vol. xvii. p. 423. See also vol. xviii. p. 276. 



j Liebig's Annalen, May 1859. 



